Automatic data collection device, method and article

ABSTRACT

A radio frequency identification system comprises a radio-frequency identification substrate and an interrogator. In one embodiment, the radio-frequency identification substrate comprises a plurality of radio-frequency identification devices. In one embodiment, a controller on the substrate controls a first one of the plurality of radio-frequency identification devices based on a state of a second one of the plurality of radio-frequency identification devices. In one embodiment, an antenna system includes an S-shaped portion electrically coupled to an integrated circuit along a central portion of the S-shaped portion. Adjusting the parameters of the segments making up the S-shaped portion controls performance characteristics of a radio-frequency identification device.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This disclosure generally relates to automatic data collection (ADC) andmore particularly to radio-frequency identification.

2. Description of the Related Art

The ADC field is generally directed to the use of devices and methodsfor automatically capturing data typically encoded in media such as amachine-readable symbol or tag carried by the item to which the datarelates. A variety of ADC devices and ADC media are ubiquitous and wellknown.

For example, a data carrier may take the form of a radio-frequencyidentification (RFID) tag, which may take the form of a card. Such tagstypically include an RFID substrate carrying a circuitry such as asemiconductor device including memory and one or more conductive tracesthat form an antenna. Typically, RFID tags act as transponders,providing information stored in the semiconductor device in response toa radio-frequency (RF) signal, commonly referred to as an interrogationsignal, received at the antenna from a reader or interrogator. Some RFIDtags include security measures, such as passwords and/or encryption.Many RFID tags also permit information to be written or stored in thesemiconductor memory via an RF signal.

RFID tags that include a discrete power source, for example a battery,are commonly referred to as active devices. RFID devices that rely on anRF signal to derive power are commonly referred to as passive devices.RFID tags may employ both active and passive power sources.

Identification of an RFID device or tag generally depends on RF energyproduced by a reader or interrogator arriving at the RFID tag andreturning to the interrogator. In general, lower frequencies canpenetrate objects better than higher frequencies, but higher frequenciescan carry more data than lower frequencies. In addition, multipleprotocols exist for use with RFID tags. These protocols may specify,among other things, particular frequencies, frequency ranges, modulationschemes, security schemes, and data formats. Conventional approachesemploy multiple RFID tags, each tag using a frequency band and protocolsuited to a particular application.

BRIEF SUMMARY OF THE INVENTION

In one aspect, a radio-frequency identification substrate comprises afirst radio-frequency identification device, a second radio-frequencyidentification device, and a controller communicatively coupled to thefirst radio-frequency identification device and to the secondradio-frequency identification device and configured to control thefirst radio-frequency identification device based at least in part on astate of the second radio-frequency device.

In one embodiment, the controller is further configured to control thesecond radio-frequency device based at least in part on a state of thefirst radio frequency device.

In one embodiment, the state of the second radio-frequencyidentification device is based at least in part on whether the secondradio-frequency device has detected a radio-frequency signal. In oneembodiment, the controller is configured to activate the firstradio-frequency identification device in response to the detection ofthe radio-frequency signal by the second radio-frequency identificationdevice.

In one embodiment, the controller is configured to control at least oneof the radio-frequency identification devices based at least in part ona power signal. In one embodiment, the controller is configured tocontrol at least one of the radio-frequency identification devices basedat least in part on a signal indicating an amount of data stored in amemory. In one embodiment, the controller is configured to control atleast one of the radio-frequency identification devices based at leastin part on a signal indicating a data transmission was not successful.

In one embodiment, the first radio-frequency identification device isconfigured to operate in accordance with a first protocol and the secondradio-frequency device is configured to operate in accordance with thefirst protocol.

In one embodiment, the first radio-frequency identification devicecomprises a first integrated circuit, and a first antenna systemelectrically coupled to the first integrated circuit. In one embodiment,the first integrated circuit comprises a memory, and a power source. Inone embodiment, the first antenna system comprises a parasitic element.In one embodiment, the first antenna system comprises a rectilinearportion. In one embodiment, the first antenna system comprises a curvedportion. In one embodiment, the first antenna system comprises a firstarm electrically coupled to the first integrated circuit, and a secondarm electrically coupled to the first integrated circuit. In oneembodiment, the first antenna system has an inner perimeter and thesecond radio-frequency identification device is contained within an areadefined by the inner perimeter of the first antenna system. In oneembodiment, the second radio-frequency identification device comprises asecond integrated circuit, and a second antenna system electricallycoupled to the second integrated circuit. In one embodiment, the secondradio-frequency identification device comprises a second antenna systemelectrically coupled to the first integrated circuit.

In one embodiment, the first radio-frequency identification devicecomprises a first integrated circuit, and a first antenna systemcomprising a first convex portion electrically coupled to the firstintegrated circuit, and a second convex portion electrically coupled tothe first integrated circuit. In one embodiment, the first convexportion and the second convex portion are configured to form an S-shapedportion of the first antenna system, the first antenna system beingelectrically coupled to the first integrated circuit between the firstand second convex portions. In one embodiment, the S-shaped portion isrectilinear. In one embodiment, the S-shaped portion comprises a curvedportion.

In one embodiment, the second radio frequency identification devicecomprises a second antenna system electrically coupled to the firstintegrated circuit. In one embodiment, the second antenna systemcomprises a third convex portion electrically coupled to the firstintegrated circuit, and a fourth convex portion electrically coupled tothe first integrated circuit, wherein the first convex portion and thesecond convex portion are configured to form a first S-shaped portion ofthe first antenna system, the first antenna system being electricallycoupled to the first integrated circuit along a central portion of thefirst S-shaped portion, and the third convex portion and the fourthconvex portion are configured to form a second S-shaped portion of thesecond antenna system, the second antenna system being electricallycoupled to the first integrated circuit along a central portion of thesecond S-shaped portion.

In one embodiment, the first radio-frequency identification device isconfigured to operate in accordance with a first communication protocoland the second radio-frequency identification device is configured tooperate in accordance with a second communication protocol. In oneembodiment, the first radio-frequency identification device isconfigured to operate at a first resonant frequency and the secondradio-frequency identification device is configured to operate at asecond resonant frequency different from the first resonant frequency.

In another aspect, a radio-frequency identification system comprises aninterrogator operable to produce an interrogation signal, and asubstrate comprising first means for responding to the interrogationsignal, second means for responding to the interrogation signal, andmeans for controlling the first means for responding to theinterrogation signal based at least in part on a state of the secondmeans for responding to the interrogation signal.

In one embodiment, the means for controlling is configured to controloperation of the second means for responding to the interrogation signalbased at least in part on a state of the first means for responding tothe interrogation signal.

In one embodiment, the first means for responding to the interrogationsignal comprises a first integrated circuit, and a first antenna systemelectrically coupled to the first integrated circuit, wherein the firstantenna system has an inner perimeter and the second means forresponding is contained within an area on the substrate defined by theinner perimeter of the first antenna system. In one embodiment, thefirst means for responding to the interrogation signal comprises a firstintegrated circuit, and a first antenna system comprising a first convexportion, and a second convex portion, wherein the first convex portionand the second convex portion are configured to form an S-shaped portionof the first antenna system, the first antenna system being electricallycoupled to the first integrated circuit between the first convex portionand the second convex portion.

In one embodiment, the first means for responding to the interrogationsignal is configured to operate in accordance with a first communicationprotocol and the second means for responding to the interrogation signalis configured to operate in accordance with a second communicationprotocol. In one embodiment, the first means for responding to theinterrogation signal is configured to operate at a first resonantfrequency and the second means for responding to the interrogationsignal is configured to operate at a second resonant frequency differentfrom the first resonant frequency.

In another aspect, a method of controlling a first radio-frequencyidentification device on a substrate comprises determining, on thesubstrate, a state of a second radio-frequency identification device onthe substrate, generating, on the substrate, a control signal based atleast in part on the determined state of the second radio-frequencyidentification device, and controlling the first radio-frequencyidentification device on the substrate based at least in part on thecontrol signal. In one embodiment, determining the state of the secondradio-frequency identification device comprises determining whether aninterrogation signal has been received by the second radio-frequencyidentification device. In one embodiment, determining the state of thesecond radio-frequency identification device comprises determining astate of a memory. In one embodiment, determining a state of the secondradio-frequency device comprises determining a state of a power supply.

In one embodiment, the method further comprises controlling the secondradio-frequency identification device based at least in part on a stateof the first radio-frequency identification device. In one embodiment,controlling the first radio-frequency identification device comprisesenabling the first radio-frequency identification device in response toreceipt of the interrogation signal by the second radio-frequencyidentification device. In one embodiment, the method further comprisesdisabling the first radio-frequency identification device when a firstcriteria is satisfied.

In another aspect, a method of operating a radio-frequencyidentification system comprises receiving a first response signal from afirst radio-frequency identification device of a radio-frequencyidentification tag in response to an interrogation signal, when thefirst response signal is received, processing the first response signal,determining whether a second response signal is received from a secondradio-frequency identification device of the radio-frequencyidentification tag, and when the first response signal is received andit is determined that the second response signal is not received,initiating error processing. In one embodiment, the first responsesignal is in a first frequency range and the second response signal isin a second frequency range different from the first frequency range. Inone embodiment, the first frequency range is lower than the secondfrequency range. In one embodiment, the interrogation signal comprises afirst component signal at a first frequency and a second componentsignal at a second frequency different from the first frequency. In oneembodiment, determining whether the second response signal is receivedcomprises determining whether the second response signal is receivedwithin a defined period of time of receipt of the first response signal.

In another aspect, a radio-frequency identification substrate comprisesa first radio-frequency identification device on the substrate andconfigured to operate in accordance with a first communication protocol,and a second radio-frequency identification device on the substrate andconfigured to operate in accordance with a second communication protocoldifferent from the first communication protocol. In one embodiment, thefirst radio-frequency identification device comprises a first integratedcircuit, and a first antenna system electrically coupled to the firstintegrated circuit. In one embodiment, the first integrated circuitcomprises a data system, and a power system. In one embodiment, thefirst antenna system comprises a parasitic element. In one embodiment,the first antenna system comprises a first antenna trace, and a secondantenna trace electrically coupled to the first antenna trace andextending from the first antenna trace in a direction approximatelyperpendicular to the first antenna trace. In one embodiment, the firstantenna system has an inner perimeter and the second radio-frequencyidentification device is contained within an area on the substratedefined by the inner perimeter of the first antenna system. In oneembodiment, the second radio-frequency identification device comprises asecond integrated circuit, and a second antenna system electricallycoupled to the second integrated circuit.

In one embodiment, the substrate further comprises a controller on thesubstrate communicatively coupled to the first and secondradio-frequency identification devices and configured to control atleast one of the radio-frequency identification devices.

In one embodiment, the first radio-frequency identification devicecomprises a first integrated circuit, and a first antenna systemcomprising a first convex portion electrically coupled to the firstintegrated circuit, and a second convex portion electrically coupled tothe first integrated circuit. In one embodiment, the first convexportion and the second convex portion are configured to form an S-shapedportion of the first antenna system, the first antenna system beingelectrically coupled to the first integrated circuit between the firstconvex portion and the second convex portion. In one embodiment, theS-shaped portion is rectilinear. In one embodiment, the first convexportion comprises a first segment electrically coupled to the firstintegrated circuit and extending from the integrated circuit in a firstdirection, and a second segment electrically coupled to the firstsegment and extending from the first segment in second directiongenerally perpendicular to the first direction. In one embodiment, thesecond radio frequency identification device comprises a second antennasystem electrically coupled to the first integrated circuit. In oneembodiment, the second antenna system comprises a third convex portion,and a fourth convex portion, wherein the first convex portion and thesecond convex portion are configured to form a first S-shaped portion ofthe first antenna system, the first antenna system being electricallycoupled to the first integrated circuit between the first convex portionand the second convex portion, and the third convex portion and thefourth convex portion are configured to form a second S-shaped portionof the second antenna system, the second antenna system beingelectrically coupled to the first integrated circuit between the thirdconvex portion and the fourth convex portion.

In one embodiment, the first radio-frequency identification device andthe second radio-frequency identification device share a common memory.In one embodiment, the first radio-frequency identification device isconfigured to operate at a first resonant frequency and the secondradio-frequency identification device is configured to operate at asecond resonant frequency different from the first resonant frequency.

In another aspect, a radio-frequency identification device comprises anintegrated circuit, and a first antenna system comprising a firstS-shaped portion, the first S-shaped portion comprising a first convexportion, and a second convex portion, wherein the first S-shaped portionis electrically coupled to the integrated circuit between the firstconvex portion and the second convex portion of the first S-shapedportion. In one embodiment, the first S-shaped portion is rectilinear.In one embodiment, the first S-shaped portion comprises a curvedportion. In one embodiment, the first antenna system further comprises aparasitic element.

In one embodiment, the first convex portion comprises a first segmentelectrically coupled to the integrated circuit, extending from theintegrated circuit in a first direction, and having a first width and afirst length, a second segment electrically coupled to the firstsegment, extending from the first segment in a second directionapproximately perpendicular to the first direction, and having a secondwidth and a second length, and a third segment electrically coupled tothe second segment, extending from the second segment in third directiongenerally opposite to the first direction, and having a third width anda third length. In one embodiment, the second convex portion comprises afourth segment electrically coupled to the integrated circuit, extendingfrom the integrated circuit in the third direction, and having a fourthwidth and a fourth length, a fifth segment electrically coupled to thefourth segment, extending from the fourth segment in a fourth directiongenerally opposite to the second direction, and having a fifth width anda fifth length, and a sixth segment electrically coupled to the fifthsegment, extending from the fifth segment in the first direction, andhaving a sixth width and a sixth length. In one embodiment, the firstwidth is equal to the fourth width, the first length is equal to thefourth length, the second width is equal to the fifth width, the secondlength is equal to the fifth length, the third width is equal to thesixth width, and the third length is equal to the sixth length. In oneembodiment, the second width is equal to the third width, and the firstlength is equal to the third length.

In one embodiment, the first convex portion comprises a copper trace. Inone embodiment, the first convex portion comprises a silver ink trace.

In one embodiment, the first convex portion comprises a first segmentelectrically coupled to the integrated circuit, extending from theintegrated circuit in a first direction, and having a first width and afirst length, and a first return segment electrically coupled to thefirst segment, extending from the first segment in a second direction,and having a second width, a second length and a first curvature. In oneembodiment, the second convex portion comprises a second segmentelectrically coupled to the integrated circuit, extending from theintegrated circuit in a third direction opposite from the firstdirection, and having a third width and a third length, and a secondreturn segment electrically coupled to the second segment, extendingfrom the first segment in a fourth direction, and having a fourth width,a fourth length and a second curvature.

In one embodiment, the first antenna system further comprises a secondS-shaped portion, the second S-shaped portion comprising a third convexportion, and a fourth convex portion, wherein the second S-shapedportion is electrically coupled to the integrated circuit between thethird convex portion and the fourth convex portion of the secondS-shaped portion. In one embodiment, the third convex portion is in aplane of the first convex portion and rotated approximately 90 degreesfrom the first convex portion with respect to the integrated circuit.

In one embodiment, the radio-frequency identification device furthercomprises a second antenna system comprising a second S-shaped portion,the second S-shaped portion comprising a third convex portion, and afourth convex portion. In one embodiment, the third convex portion is ina plane of the first convex portion and rotated with respect to thefirst convex portion. In one embodiment, the third convex portion isrotated ninety degrees with respect to the first convex portion. In oneembodiment, the second S-shaped portion is electrically coupled to theintegrated circuit between the third convex portion and the fourthconvex portion of the second S-shaped portion.

In another aspect, a method of making a radio-frequency identificationdevice comprises printing a first convex portion of an S-shaped portionof an antenna system on a substrate, printing a second convex portion ofthe S-shaped portion of the antenna system on the substrate, andelectrically coupling the antenna system to an integrated circuitbetween the first convex portion and the second convex portion of theantenna system. In one embodiment, printing the first convex portioncomprises printing a first segment extending in a first direction andhaving a first width and a first length, printing a second segmentextending from the first segment in a second direction approximatelyperpendicular to the first direction and having a second width and asecond length, and printing a third segment extending from the secondsegment in a third direction opposite from the first direction andhaving a third width and a third length. In one embodiment, modifyingthe first length modifies a performance characteristic of theradio-frequency identification device.

In another aspect, a system for manufacturing a radio-frequencyidentification device comprises means for printing segments of anantenna system on a substrate and means for controlling the means forprinting configured to control the width, length and direction ofsegments printed by the means for printing and to cause the means forprinting to print segments forming first and second convex portions ofthe antenna system, the first and second convex portions forming anS-shaped portion of the antenna system, the S-shaped portion configuredfor electrical coupling between the first and second convex portions. Inone embodiment, the means for printing comprises a trace printeroperable to deposit a conductive ink on selected portions of thesubstrate.

In another aspect, a computer-readable memory medium stores instructionsfor causing a control system to control a trace printer by generatingcontrol signals causing the trace printer to print a first convexantenna trace on a substrate, and print a second convex antenna trace onthe substrate, wherein the first convex antenna trace and the secondconvex antenna trace together form a first S-shaped portion of anantenna system, the first S-shaped portion adopted for electricalcoupling of the antenna system between the first and second convexantenna traces. In one embodiment, the stored instructions includeinstructions for generating control signals to cause the trace printerto print a first segment of the first convex antenna trace, the firstsegment having a first width and a first length and extending in a firstdirection, print a second segment of the first convex antenna trace, thesecond segment having a second width and a second length and extendingfrom an end portion of the first segment in a second directionperpendicular to the first direction, and print a third segment of thefirst convex antenna trace, the third segment having third width and athird length and extending from an end portion of the second segment ina third direction opposite of the first direction. In one embodiment,the stored instructions include instructions for generating controlsignals to cause the trace printer to print a first segment of the firstconvex antenna trace, the first segment having a first width and a firstlength and extending in a first direction, and print a first returnsegment of the first convex antenna trace, the first return segmentextending from an end portion of the first segment in a seconddirection, and having a second width, a second length and a firstcurvature. In one embodiment, the stored instructions further includeinstructions for generating control signals to cause the trace printerto print a third convex antenna trace on the substrate, the third convexantenna trace rotated approximately 90 degrees with respect to the firstconvex antenna trace, and print a fourth convex antenna trace on thesubstrate, wherein the third convex antenna trace and the fourth convexantenna trace together form a second S-shaped portion of the antennasystem, the second S-shaped portion adopted for electrical coupling ofthe antenna system between the third and fourth convex antenna traces.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

In the drawings, identical reference numbers identify similar elementsor acts. The sizes and relative positions of elements in the drawingsare not necessarily drawn to scale. For example, the shapes of variouselements and angles are not drawn to scale, and some of these elementsare arbitrarily enlarged and positioned to improve drawing legibility.Further, the particular shapes of the elements as drawn are notnecessarily intended to convey any information regarding the actualshape of particular elements, and have been selected solely for ease ofrecognition in the drawings.

FIG. 1 is a functional block diagram of an embodiment of aradio-frequency identification system.

FIG. 2 is a functional block diagram of another embodiment of aradio-frequency identification system.

FIG. 3 is a flow diagram illustrating an embodiment of a method ofoperating a radio-frequency identification system.

FIG. 4 is a flow diagram illustrating an embodiment of a method ofoperating a radio-frequency identification system.

FIG. 5 is a flow diagram illustrating an embodiment of a method ofoperating a radio-frequency identification system.

FIG. 6 is a top plan view of an embodiment of an RFID tag.

FIG. 7 is a top plan view of an embodiment of an RFID tag.

FIG. 8 is a top plan view of an embodiment of an RFID tag.

FIG. 9 is a top plan view of an embodiment of an RFID tag.

FIG. 10 is graphical representation of performance characteristics of anRFID tag.

FIG. 11 is a top plan view of an embodiment of an RFID tag.

FIG. 12 is a cross-sectional view of the embodiment illustrated in FIG.11 taken along line A-A.

FIG. 13 is a graphical representation of the impact of modifying theantenna arm parameters of the embodiment of an RFID tag deviceillustrated in FIG. 11 on the performance characteristics of the RFIDtag.

FIG. 14 is a top plan view of an embodiment of an RFID tag.

FIG. 15 is a top plan view of an embodiment of an RFID tag.

FIG. 16 is a top plan view of an embodiment of an RFID tag.

FIG. 17 is a graphical representation of the tag range as a function offrequency for the embodiments of FIGS. 14, 15 and 16.

FIG. 18 is a top plan view of an embodiment of an RFID tag.

FIG. 19 is a top plan view of an embodiment of an RFID tag.

FIG. 20 is a top plan view of an embodiment of an RFID tag.

FIG. 21 is a top plan view of an embodiment of an RFID tag.

FIG. 22 is a top plan view of an embodiment of an RFID tag.

FIG. 23 is a top plan view of an embodiment of an RFID tag.

FIG. 24 is a top plan view of an embodiment of an RFID tag.

FIG. 25 is a functional block diagram of an embodiment of a traceprinter system.

DETAILED DESCRIPTION OF THE INVENTION

In the following description, certain details are set forth in order toprovide a thorough understanding of various embodiments of devices,methods and articles. However, one of skill in the art will understandthat other embodiments may be practiced without these details. In otherinstances, well-known structures and methods associated with RFID tags,RFID devices, RFID substrates, semiconductor devices, interrogators, RFsignals, and antennas have not been shown or described in detail toavoid unnecessarily obscuring descriptions of the embodiments.

Unless the context requires otherwise, throughout the specification andclaims which follow, the word “comprise” and variations thereof, such as“comprising,” and “comprises,” are to be construed in an open, inclusivesense, that is as “including, but not limited to.”

Reference throughout this specification to “one embodiment,” or “anembodiment” means that a particular feature, structure or characteristicdescribed in connection with the embodiment is included in at least oneembodiment. Thus, the appearances of the phases “in one embodiment,” or“in an embodiment” in various places throughout this specification arenot necessarily referring to the same embodiment, or to all embodiments.Furthermore, the particular features, structures, or characteristics maybe combined in any suitable manner in one or more embodiments to obtainfurther embodiments.

The headings are provided for convenience only, and do not interpret thescope or meaning of this disclosure or the claimed invention.

FIG. 1 is a functional block diagram of an RFID system 100 comprising anRFID tag 102, which may take the form of a card, and a reader orinterrogator 104. The RFID tag 102 comprises an RFID substrate 103comprising a first RFID device or module 106, a second RFID device ormodule 108 and a controller 110. The first RFID device 106 iscommunicatively coupled to the second RFID device 108 by the controller110. The controller 110 may be configured to use a state of the RFID tag102, such as a state of the first RFID device 106, to control operationof the RFID tag 102. For example, the RFID tag 102 may use a state ofthe first RFID device 106 to control operation of the second RFID device108, to use a state of the second RFID device 108 to control operationof the first RFID device 106, to use a state of both RFID devices tocontrol operation of one of the RFID devices, and/or to use a state ofboth RFID device to control operation of both RFID devices. For example,the first RFID device 106 may be configured to detect the presence orabsence of RF energy in a particular band, such as a high-frequency RFband, and the controller 110 may be configured to activate or deactivatethe second RFID device 108 in response to the detection by the firstRFID device 106.

The first RFID device 106 as illustrated comprises an antenna system112, which as illustrated comprises an antenna, a power system 114,which as illustrated comprises an optional rectifier 116 and an optionalbattery 118, and a data system 120, which as illustrated comprises aprocessor 122 and a memory 124. The antenna system 112 sends andreceives radio frequency signals and may comprise multiple antennas,multiple antenna arms, and parasitic elements, as illustrated by theexamples discussed in more detail below. The power system 114 providespower to the first RFID device 106 and may be configured to providepower in a passive and/or an active manner. The data system 120 isconfigured to generate output signals in response to signals receivedfrom the antenna system 112 and/or the controller 110. In someembodiments, the data system 120 may comprise discrete circuitry inaddition to, or instead of, the illustrated processor 122 and/or thememory 124.

The second RFID device 108 as illustrated comprises an antenna system126, which as illustrated comprises an antenna, a power system 128,which as illustrated comprises a rectifier 130 and a battery 132, and adata system 134, which as illustrated comprises a processor 136 and amemory 138. The antenna system 126 sends and receives radio frequencysignals and may comprise multiple antennas, multiple antenna arms, andparasitic elements, as illustrated by the examples discussed in moredetail below. The power system 128 provides power to the second RFIDdevice 108 and may be configured to provide power in a passive and/or anactive manner. The data system 134 is configured to generate outputsignals in response to signals received from the antenna system 126and/or from the controller 110. In some embodiments, the data system 134may comprise discrete circuitry in addition to, or instead of, theillustrated processor 136 and/or the memory 138.

The controller 110 as illustrated comprises a processor 140, a memory142 and discrete circuitry 144, such as a switch and/or an RC circuit.In some embodiments, the controller 110 may comprise only discretecomponents. The controller 110 may draw power from one or both of theRFID devices 106, 108, may have its own passive and/or active powersystem, and/or the controller 110 may be incorporated into one of theRFID devices 106, 108.

The RFID devices 106, 108 and the controller 110 of the RFID tag 102need not have separate antenna systems, power systems and data systems,but may, for example, share one or more modules and/or systems in someembodiments. For example, a single processor and a shared memory may beemployed in some embodiments with the RFID devices 106, 108 and thecontroller 110 implemented as software stored in the memory, which mayconsist of separately identifiable subroutines. The power systems 114,128, need not have both active and passive sources. For example, thepower system 114 of the first RFID device 106 may have a passive powersource while the power system 128 of the second RFID device 108 may havean active power source.

FIG. 2 is a schematic diagram of an embodiment of an RFID tag 202. TheRFID tag 202 comprises a substrate 203, a first RFID device or module206, a second RFID device or module 208 and a controller 210. The firstRFID device 206 comprises a high-frequency antenna 212 electricallycoupled to a rectifier 216, and a data system 220.

The controller 210 comprises discrete circuitry 244. The discretecircuitry 244 comprises a diode 246, an RC circuit 248 and a switch 250.The diode 246 is coupled to the rectifier 216 at a first end 252 and tothe RC circuit 248 at a second end 254. The RC circuit 248 comprises acapacitor 256 and a resistor 258 coupled in parallel between the secondend 254 of the diode 246 and a reference voltage. The switch 250 iscontrolled by a signal taken off the second end 254 of the diode 246.

The second RFID device 208 comprises a low-frequency antenna system 226comprising a second capacitor 260 and an inductor 262 coupled inparallel across the switch 250 and at one end 263 to the referencevoltage. The embodiment of an RFID tag 202 illustrated in FIG. 2 may beadvantageously employed to detect whether a high-frequency responsesignal from the RFID tag 202 has not been received by an interrogator(see interrogator 104 in FIG. 1), for example, by using the methoddescribed below with respect to FIG. 4.

FIG. 3 is a flow diagram illustrating a method of operating an RFIDsystem, such as the RFID system 100 illustrated in FIG. 1, to controloperation of a first RFID device, such as RFID device 106, based on astate of the first RFID device 106, and on a state of the second RFIDdevice 108. The method starts at 300 and proceeds to 302.

At 302, the system 100 determines a state of operation of the first RFIDdevice 106. The state of the first RFID device 106 may be determined,for example, by the presence or absence of a signal received by thefirst RFID device 106, a value stored in the memory 124 of the firstRFID device 106, the presence or absence of a signal from the powersystem 114, such as a signal indicating a level of available power, asignal from the data system 120, such as a signal indicating an amountof data stored in the memory 124 or a signal indicating data stored inthe memory 124 has been successfully transferred, or has not beensuccessfully transferred, an indication the first RFID device 106 hasfailed, and/or by various combinations thereof. The method proceeds from302 to 304.

At 304, the system 100 determines a state of operation of the secondRFID device 108. The state of the second RFID device 108 may bedetermined, for example, by the presence or absence of a signal receivedby the second RFID device 108, a value stored in the memory 138 of thesecond RFID device 108, the presence or absence of a signal from thepower system 128, such as a signal indicating a level of availablepower, a signal from the data system 134, such as a signal indicating anamount of data stored in the memory 138 or a signal indicating datastored in the memory 138 has been successfully transferred, or has notbeen successfully transferred, an indication that the second RFID device108 has failed, and/or by various combinations thereof. The methodproceeds from 304 to 306.

At 306, the system 100 generates control signals to cause the first RFIDdevice 106 to operate in a desired manner based on the state of thefirst RFID device 106 determined at 302 and the state of the second RFIDdevice determined at 304. A look-up table may be employed to generatethe control signals. The control signals may be generated by thecontroller 110, by the first RFID device 106, by the second RFID device108, by the interrogator 104, and/or by combinations thereof. The mannerof operation of the first RFID device 106 may include, for example, nooperation, a low-power mode of operation, a high-power mode ofoperation, operation in accordance with a first communication protocol,operation in accordance with a second communication protocol, operationin first frequency band, and/or operation in a second frequency band.The method proceeds from 306 to 308, where the method terminates.

The system 100 of FIG. 1 can be used, for example, to prevent a firstfrequency RFID signal, such as a high-frequency RFID signal, from beingmissed by an interrogator when a second frequency RFID signal, such as alow-frequency RFID signal, would be detected. FIG. 4 is a flow diagramillustrating a method for using an embodiment, such as the embodiment ofFIG. 1, to prevent a first frequency RFID device, such as the RFIDdevice 106 of RFID tag 102, from being missed by an interrogator, suchas the interrogator 104. For example, an individual wearing or an itembearing an RFID tag might pass an interrogator and a high-frequencyresponse signal from the RFID tag would not be received by theinterrogator. The signal could be blocked, for example, by anotherperson or another RFID tag signal.

The method starts at 400 and proceeds to 402. At 402, the interrogator104 transmits an interrogation signal directed to the RFID tag 102. Theinterrogation signal may be, for example, a high frequency signaldirected to the first RFID device 106, a low-frequency signal directedto the second RFID device 108, or may contain more than one componentinterrogation signal. The method proceeds to 404. At 404, the system 100determines whether the interrogation signal has been received by theRFID tag 102. If an interrogation signal has not been received by theRFID tag 102 at 404, the method returns to 404.

If the interrogation signal has been received at 404, the methodproceeds to 406, where the first RFID device 106 begins transmitting afirst response signal. The method proceeds to 408, where the second RFIDdevice 108 begins transmitting a second response signal. The methodproceeds from 408 to 410. At 410, the system 100 determines whether thesecond response signal has been received by the interrogator 104. If thesecond response signal has been received by the interrogator 104, themethod proceeds to 412.

If the second response signal has not been received by the interrogator104 at 410, the method returns to 410. In some embodiments, instead ofreturning to 410, the method may return to 402 and the system mayretransmit the interrogation signal or the method may proceed to 416 forerror processing.

At 412, the system 100 determines whether the first response signal hasbeen received by the interrogator 104. If the system 100 determines thefirst response signal has been received by the interrogator 104, themethod proceeds to 414, where the system 100 processes the firstresponse signal. The method then terminates at 418.

If the system 100 determines at 412 that the first response signal hasnot been received by the interrogator 104, the method proceeds to 416,for error processing. For example, the system 100 may sound an alarm(not shown) or the method may return to 402 for retransmission of theinterrogation signal by the system 100. The method then terminates at418.

FIG. 5 is a flow diagram illustrating a method for conserving batterypower of an RFID tag, such as the RFID tag 102 of FIG. 1. The methodstarts at 500 and proceeds to 502, where the interrogator 104 transmitsan interrogation signal. The method proceeds to 504, where the system100 determines whether the interrogation signal has been received by thefirst RFID device 106, which may be a passive RFID device. If the system100 determines at 504 that the interrogation signal has not beenreceived by the first RFID device 106, the method returns to 504.

If the system 100 determines the interrogation signal has been receivedby the first RFID device 106, the method proceeds from 504 to 506, wherethe controller 110 enables the second RFID device 108, which may be anactive RFID device. Alternatively, the controller 110 may enable ahigh-power mode of the second RFID device 108. The method proceeds from506 to 508, where the system 100 determines whether a criteria fordisabling the second RFID device 108 has been satisfied, such as, forexample, a time-out period, receipt of an acknowledgement signal ordiscontinuance of the interrogation signal. If the system 100 determinesthe criteria for disabling the second RFID device 108 has not beensatisfied, the method returns to 508.

If the system 100 determines at 508 that the criteria for disabling thesecond RFID device 108 has been satisfied, the method proceeds from 508to 510, where the system 100 disables the second RFID device 108, oralternatively, the system 100 disables the high-power mode of the secondRFID device 108. The method proceeds from 510 to 512, where the methodterminates.

Embodiments of the methods discussed in FIGS. 3, 4 and 5 may containadditional acts not shown in FIGS. 3, 4 and 5, may not contain all ofthe acts shown in FIGS. 3, 4 and 5, may perform acts shown in FIGS. 3, 4and 5 in various orders, and may combine acts shown in FIGS. 3, 4 and 5.For example, the embodiment illustrated in FIG. 3 may be modified togenerate control signals to control operation of the first RFID device106 based solely on the state of the second RFID device 108. In anotherexample, the embodiment illustrated in FIG. 5 may be modified todetermine whether other criteria are satisfied before enabling thesecond RFID device at 506. For example, there may be no data to transmitor insufficient data to justify the use of a higher power level or ahigher frequency RFID device, or the conditions may be such that ahigh-frequency signal would not be received by the interrogator 104.

FIG. 6 is a top plan view of an embodiment of an RFID tag 602 comprisinga first RFID device 606, a second RFID device 608 and a third RFIDdevice 664 on a substrate 603 in a single casing or package 666. Thesecond RFID device 608 and the third RFID device 664 are containedwithin an area on the substrate 603 defined by the first RFID device606. The RFID devices 606, 608, 664 can employ separate antenna systems(see antenna system 112 of FIG. 1), or may employ a common antennasystem. The RFID devices 606, 608, 664 may comprise separate integratedcircuits or chips, or may share a single chip. The RFID devices 606,608, 664 may be configured to operate in different frequency bands usingdifferent protocols as desired, or may be configured to operate underthe same protocol and/or combinations thereof. For example, the firstRFID device 606 may be configured to operate in accordance with a firstprotocol, while the second RFID device 608 and the third RFID device 664are configured to operate in accordance with a second protocol,different from the first protocol.

FIG. 7 is a top plan view of an embodiment of an RFID tag 702 comprisinga substrate 703 comprising a first RFID device 706 comprising a firstintegrated circuit or chip 770 and a first antenna system 712 containedwithin a package 766. A second RFID device 708 comprising a secondintegrated circuit or chip 772 and a second antenna system 726 iscontained within an area 774 defined by the first RFID device 706. Thefirst RFID device 706 and the second RFID device 708 may be configuredto operate using different protocols and/or different frequencies. Forexample, the first RFID device 706 may be configured to operate under,for example, ISO class 0, while the second RFID device 708 is configuredto operate under, for example, ISO class 1, generation 2. In anotherexample, the first RFID device 706 may be configured to operate at, forexample, 433 MHz or 915 MHz, while the second RFID device 708 may beconfigured to operate at, for example, 134.2 KHz, 13.56 MHZ or 2.45 GHz.An RFID tag 702 as illustrated in FIG. 7 with RFID devices 706, 708configurable to operate at some of the example frequencies can beintegrated into a single substrate 703 with a length 776 of, forexample, 50 mm, and a width 778 of, for example, 50 mm, with littlemutual interference.

FIG. 8 is a top plan view of an embodiment of an RFID tag 802 comprisinga first RFID device 806 and a second RFID device 808 in a package 866.The first RFID device 806 comprises a first integrated circuit or chip870, a first antenna system 812, and a first parasitic element 880. Thesecond RFID device 808 comprises a second integrated circuit or chip 872and a second antenna system 826. The first RFID device 806 and thesecond RFID device 808 of the embodiment of FIG. 8 may also beconfigured to operate using different protocols and/or differentfrequencies, as discussed above, for example, with regard to FIG. 7, andcan be integrated into a single substrate 803 with a length 876 of, forexample, 50 mm and a width 878 of, for example, 50 mm with little mutualinterference.

FIG. 9 is a top plan view of an embodiment of an RFID tag 902 comprisinga first RFID device 906 and a second RFID device 908. The first RFIDdevice 906 comprises a first integrated circuit or chip 970 and a firstantenna system 912 having a substantially circular inner perimeter 982.The second RFID device 908 is contained within an area 983 defined bythe inner perimeter 982 of the first RFID device 906 and comprises asecond integrated circuit or chip 972 and a second antenna system 926.The first RFID device 906 and the second RFID device 908 of theembodiment of FIG. 9 may also be configured to operate using differentprotocols and/or different frequencies, as discussed above, for example,with regard to FIG. 7, and can be integrated into a single substrate 903with a length 976 of, for example, 50 mm and a width 978 of, forexample, 50 mm with little mutual interference.

Some important RFID tag performance characteristics include the peakrange of the tag, the resonant frequency of the tag, and the range widthof the tag. These characteristics are illustrated in a graphical form inFIG. 10 for a tag with a single RFID device. Frequency is plotted alongthe horizontal axis 1. Range is plotted along the vertical axis 2. Thecurve 3 represents the range of the RFID tag as a function of frequency.The peak range 4 of the RFID tag occurs at the resonant frequency 5 ofthe RFID tag. The range width 6 is the frequency bandwidth in which theRFID tag read range is above a threshold minimum 7.

FIGS. 11 and 12 illustrate an RFID tag 1102 comprising an RFID device1106. FIG. 11 is a top plan view of the RFID tag 1102. FIG. 12 is a sidecross-sectional view of the RFID tag 1102 taken along lines A-A of FIG.11. The RFID tag 1102 comprises an integrated circuit or chip 1170, andan antenna system 1112 comprising a first arm 1111 electrically coupledto the integrated circuit 1170 at a first node 1169 (see FIG. 12) and asecond arm 1113 electrically coupled to the integrated circuit 1170 at asecond node 1171 (see FIG. 12). In some embodiments, the first arm 1111and the second arm 1113 may be separately coupled to the integratedcircuit 1170, as illustrated. In some embodiments, the first arm 1111and the second arm 1113 may be electrically coupled to the integratedcircuit 1170 at a common node (not shown). As illustrated, theintegrated circuit 1170 comprises a first data system 1120 and a seconddata system 1134. As illustrated, the antenna system 1112 is generallyin a first plane 1200 parallel to a second plane 1202 of the integratedcircuit 1170.

The first arm 1111 comprises a first segment 1184, a second segment 1186and a third or return segment 1188. The first segment 1184 has a widthW1 and a length L1, the second segment 1186 has a width W2 and a lengthL2 and the third segment 1188 has a width W3 and a length L3. The secondarm 1113 comprises a first segment 1190, a second segment 1192 and athird or return segment 1194. The first segment 1190 has a width W4 anda length L4, the second segment 1192 has a width W5 and a length L5 andthe third segment 1194 has a width W6 and a length L6.

The first segment 1184 of the first arm 1111 and the first segment 1190of the second arm 1113 extend from the integrated circuit 1170 ingenerally opposite directions. That is, the first segment 1184 of thefirst arm 1111 extends from the integrated circuit 1170 in a firstdirection and the first segment 1190 of the second arm 1113 extends fromthe integrated circuit 1170 in a second direction opposite from thefirst direction with respect to the integrated circuit 1170.

Referring now to the first arm 1111, the third segment 1188 is generallyparallel to the first segment 1184 and is electrically coupled to thefirst segment 1184 through the second segment 1186. The second segment1186 extends from the first segment 1184 in a third direction generallyperpendicular to the first direction. The third segment 1188 extendsfrom the second segment 1186 generally in the second direction. Thefirst arm 1111 has an internal perimeter 1195 at least partiallysurrounding an internal area 1196 on three sides. The first arm 1111 hasa C-shape configuration forming a first convex portion 1206 of theantenna system 1112 opening in the second direction.

Referring now to the second arm 1113, the third segment 1194 isgenerally parallel to the first segment 1190 and is electrically coupledto the first segment 1190 through the second segment 1192. The secondsegment 1192 extends from the first segment 1190 in a fourth directiongenerally perpendicular to the second direction and opposite the thirddirection. The third segment 1194 extends from the second segment 1192generally in the first direction. The second arm 1113 has an internalperimeter 1197 at least partially surrounding an internal area 1198 onthree sides. The second arm 1113 has a C-shaped configuration forming asecond convex portion 1208 of the antenna system 1112 opening in thefirst direction.

Referring now to the antenna system 1112 as a whole, the antenna systemhas an S-shaped portion 1204 illustrated by a dashed line and formedfrom the first convex portion 1206 of the first arm 1111 and the secondconvex portion 1208 of the second arm 1113. The antenna system 1112 iselectrically coupled to the integrated circuit 1170 along a centralportion 1209 of the S-shaped portion 1204. The first convex portion 1206opens in the second direction and the second convex portion 1208 opensin the first direction and the antenna system 1112 is coupled to theintegrated circuit 1170 between the first convex portion 1206 and thesecond convex portion 1208 of the S-shaped portion 1204. As illustratedin FIG. 11, the S-shaped portion 1204 is rectilinear. That is, theS-shaped portion 1204 is formed of a plurality of straight segments.

A straight line B-B can be drawn in the plane 1200 of the antenna system1112 that: intersects the first segment 1184 and the third segment 1188of the first arm 1111 of the antenna system 1112; does not intersect thesecond segment 1186 of the first arm 1111; and does not intersect thefirst segment 1190 of the second arm 1113. A second straight line C-Ccan be drawn that: intersects the first segment 1190 and the thirdsegment 1194 of the second arm 1113 of the antenna system 1112; does notintersect the second segment 1192 of the second arm 1113; and does notintersect the first segment 1184 of the first arm 1111.

The RFID tag 1102 resonant frequency can be controlled by adjusting thelengths L1-L6 of the segments 1184-1194 of the arms 1111, 1113 of theantenna system 1112. The gain of the antenna system 1112 can becontrolled by adjusting the ratio of the length of the first segments1184, 1190 to the length of the third segments 1188, 1194, and reaches amaximum when:

L3=2(L1)=L6=2(L4)  (Eq. 1).

The reactance or inductance of the antenna system 1112 can be controlledby adjusting the lengths L1, L4 and widths W1, W4 of the first segments1184, 1190. Adjusting the lengths L1, L4 and widths W1, W4 of the firstsegments 1184, 1190 will also impact the gain of the antenna system1112.

The resistance of the antenna system 1112 can be controlled by adjustingthe lengths L2, L5 of the second segments 1186, 1192. The rangewidth ofthe antenna system 1112 can be controlled by adjusting the widths W2,W3, W5, W6 of the second segments 1186, 1192 and the third segments1188, 1194. The antenna system 1112 can be tuned by adjusting thelengths L3, L6 of the third segments 1188, 1194 and the widths W2, W5 ofthe second segments 1186, 1192. For example, the antenna system 1112 canbe tuned to a higher frequency by reducing the lengths L3, L6 of thethird segments 1188, 1194. In another example, the antenna system 1112can be tuned to a lower frequency by reducing the widths W2, W5 of thesecond segments 1186, 1192.

In some embodiments, the first arm 1111 and the second arm 1113 havesegments 1184, 1186, 1188, 1190, 1192, 1194 with the same or similarlengths and widths. For example, in some embodiments,

L1=L4  (Eq. 2)

L2=L5  (Eq. 3)

L3=L6  (Eq. 4)

W1=W4  (Eq. 5)

W2=W5  (Eq. 6)

W3=W6  (Eq. 7).

In other embodiments, the arms 1111, 1113 of the antenna system 1112 maynot be symmetrical, which facilitates dual-band operation of the RFIDtag 1102.

FIG. 13 is a graphical representation of the effects of replacing someof the parameters L1-L6 and W1-W6 on the performance characteristics ofan RFID tag. Frequency is plotted along the horizontal axis 1. Range isplotted along the vertical axis 2. A first curve 3 represents the rangeof the RFID tag for a given set of parameter values as a function offrequency. The peak range 4 of the RFID tag occurs at the resonantfrequency 5 of the RFID tag. The range width 6 is the frequencybandwidth in which the RFID tag read range is above a threshold minimum7.

A second curve 8 illustrates the impact of reducing the widths W2, W5 ofthe second segments 1186, 1192 of the arms 1111, 1113 of the antennasystem 1112 illustrated in FIGS. 11 and 12. The peak range 9 isincreased. The resonant frequency 10 is decreased and the range width 11is decreased.

A third curve 12 illustrates the impact of decreasing the lengths L3, L6of the third segments 1188, 1194 of the arms 1111, 1113 of the antennasystem 1112. The peak range 13 is decreased. The resonant frequency 14is increased and the range width 15 is increased.

FIG. 14 is a top plan view of an embodiment of an RFID tag 1402.Measurements were taken with an embodiment as illustrated in FIG. 14constructed using a single-sided, 2 mil. polyester substrate 1403, aPhilips G2 RFID integrated circuit 1470 and flip-chip packaging, with,

L1=L4=40 mm  (Eq. 8)

L2=L5=30 mm  (Eq. 9)

L3=L6=55 mm  (Eq. 10)

W1=W4=3 mm  (Eq. 11)

W2=W5=10 mm  (Eq. 12)

W3=W6=10 mm  (Eq. 13).

A silver ink trace (using ink sold by DuPont under the trade designation5025) was printed on the substrate 1403 to form the arms 1411, 1413 ofthe antenna system 1412. The antenna system 1412 has approximatedimensions of 80 mm by 83 mm. Performance of the embodiment of FIG. 14was measured with the embodiment placed inside a label (not shown) andaffixed to a cardboard box (not shown). This represents a typicalapplication of an RFID tag in a conventional shipping label. Theembodiment was found to have a sixteen-foot peak range at a resonantfrequency of 910 MHz and a range width from 860 to 960 MHz for aten-foot minimum range when measured normal to a plane (see plane 1200of FIG. 12) of the antenna system 1412.

A straight line B-B can be drawn which: intersects the first segment1484 and the third segment 1488 of the first arm 1411 and the thirdsegment 1494 of the second arm 1413 of the antenna system 1412; does notintersect the second segment 1486 of the first arm 1411; and does notintersect the first segment 1490 of the second arm 1413. A secondstraight line C-C can be drawn which: intersects the first segment 1490and the third segment 1494 of the second arm 1413 and the third segment1488 of the first arm 1411 of the antenna system 1412; does notintersect the second segment 1492 of the second arm 1413; and does notintersect the first segment 1484 of the first arm 1411.

FIG. 15 is a top plan view of an embodiment of an RFID tag 1502.Measurements were taken with an embodiment as illustrated in FIG. 15constructed using a single-sided, 2 mil. polyester substrate 1503, aPhilips G2 RFID integrated circuit 1570 and flip-chip packaging, with,

L1=L4=40 mm  (Eq. 14)

L2=L5=30 mm  (Eq. 15)

L3=L6=40 mm  (Eq. 16)

W1=W4=0.5 mm  (Eq. 17)

W2=W5=10 mm  (Eq. 18)

W3=W6=10 mm  (Eq. 19).

One ounce copper trace material was printed on the substrate 1503 toform the arms 1511, 1513 of the antenna system 1512. The antenna system1512 of the illustrated embodiment has approximate dimensions of 80 mmby 80 mm. Performance of the embodiment of FIG. 15 was measured with theembodiment placed inside a label (not shown) and affixed to a cardboardbox (not shown). This represents a typical application of an RFID tag ina conventional shipping label. The embodiment was found to have aneighteen-foot peak range at a resonant frequency of 910 MHz and a rangewidth from 860 to 960 MHz for a twelve-foot minimum range when measurednormal to a plane (see plane 1200 of FIG. 12) of the antenna system1512.

FIG. 16 is a top plan view of an embodiment of an RFID tag 1602.Measurements were taken with an embodiment as illustrated in FIG. 16constructed using a single-sided, 2 mil. polyester substrate 1603, aPhilips G2 RFID integrated circuit 1670 and flip-chip packaging, with,

L=96 mm  (Eq. 20)

W1=0.5 mm  (Eq. 21)

W2=28 mm  (Eq. 22)

One ounce copper trace material was printed on the substrate 1603 toform the arms 1611, 1613 of the antenna system 1612. Performance of theembodiment of FIG. 16 was measured with the embodiment placed inside alabel (not shown) and affixed to a cardboard box (not shown). Thisrepresents a typical application of an RFID tag in a conventionalshipping label. The embodiment was found to have a twenty one-foot peakrange at a resonant frequency of 910 MHz and a range width from 860 to960 MHz for a fifteen-foot minimum range when measured normal to a plane(see plane 1200 of FIG. 12) of the antenna system 1612.

FIG. 17 is a graphical representation of experimentally measured tagrange as a function of frequency for the embodiments illustrated inFIGS. 14-16. The same resonant frequency of 910 MHz is obtained byadjusting the parameters of the antenna system (i.e., by adjusting L1-L6and/or W1-W6 of the embodiment illustrated in FIG. 14). The measurementswere taken by placing the embodiments in a label (not shown) andaffixing the label to a cardboard box (not shown), which represents atypical application for an RFID tag. Similar measurements for an RFIDtag in a different application (for example, if placed in a label andaffixed to a different material) would show some variability in theresonant frequency and range measurements. The parameters of the antennasystem can be adjusted to achieve the desired RFID tag resonantfrequency and range.

Frequency is plotted along the horizontal axis 20. Range is plottedalong the vertical axis 22. A first curve 24 illustrates the range as afunction of frequency of the embodiment of an RFID tag 1402 illustratedin FIG. 14, which has an S-shaped antenna system printed withsilver-ink, under the test conditions. A second curve 26 illustrates therange as a function of frequency of the embodiment of an RFID tag 1502illustrated in FIG. 15, which can be generally described as having anS-shaped antenna system printed with copper traces of a medium width,under the test conditions. A third curve 28 illustrates the range as afunction of frequency of the embodiment of an RFID tag 1602 illustratedin FIG. 16, which can be generally described as having an S-shapedantenna system printed with copper traces of a large width, under thetest conditions.

Table 1, set forth below, contains data gathered during testing of theembodiments of FIGS. 14, 15 and 16. The first column of Table 1 setsforth the frequency in MHz. The remaining columns of Table 1 set forththe range in feet for the corresponding embodiment.

TABLE 1 Frequency FIG. 14 FIG. 15 FIG. 16 860 10.5 11.5 14.9 870 12.212.8 16.6 880 13.5 14.8 18 890 14.8 16.5 19.7 900 15.8 17.7 21 910 15.918 21.2 920 15.1 17.3 20.6 930 14.2 16.3 20 940 13.3 15.1 18.8 950 12.213.5 17 960 10.9 12.3 15.8

FIG. 18 is a top plan view of an embodiment of an RFID tag 1802comprising an integrated circuit 1870 electrically coupled to an antennasystem 1812 comprising a first arm 1811, a second arm 1813 and twoparasitic elements 1880 placed outside second segments 1886, 1892, thirdsegments 1888, 1894 and fourth segments 1891,1893 of the respectivefirst and second arms 1811, 1813. The first, second and third segments1884, 1886, 1888 of the first arm 1811 form a first convex portion 1833.The first, second and third segments 1890, 1892, 1894 of the second arm1813 form a second convex portion 1837. The first and second convexportions 1833, 1837 form an S-shaped portion 1835 of the antenna system1812.

FIG. 19 is a top plan view of an embodiment of an RFID tag 1902.Measurements were taken with an embodiment as illustrated in FIG. 19constructed using a single-sided, 2 mil. polyester substrate 1903, aPhilips G2 RFID integrated circuit 1970 and flip-chip packaging,wherein,

L1=L4=40 mm  (Eq. 23)

L2=L5=30 mm  (Eq. 24)

L3=L6=40 mm  (Eq. 25)

W1=W4=0.5 mm  (Eq. 26)

W2=W5=10 mm  (Eq. 27)

W3=W6=10 mm  (Eq. 28).

One ounce copper trace material was printed on the substrate 1903 toform the arms 1911, 1913 of the antenna system 1912. A parasitic ringelement 1980 printed on the substrate 1903 with one ounce copper tracematerial surrounds the arms 1911, 1913 of the antenna system 1912. Theparasitic ring element 1980 has a thickness W7 of 5 mm and is separatedfrom the arms 1911, 1913 by a distance W8 of 1 mm. The antenna system1912 has approximate dimensions of 92 mm by 92 mm. Performance of theembodiment of FIG. 19 was measured in free space normal to a plane (SeeFigure plane 1200 of FIG. 12) of the antenna system 1912. The embodimentwas found to have a twenty-eight foot peak range at a resonant frequencyof 880 MHz. Performance of the embodiment was also measured with theembodiment placed in a label (not shown) affixed to a cardboard box (notshown). The embodiment was found to have a twenty-three foot peak rangeat a resonant frequency of 830 MHz when measured normal to a plane (seeplane 1200 of FIG. 12) of the antenna system 1912. The embodiment ofFIG. 19 for which measurements were taken is identical to the embodimentof FIG. 15 for which measurements were taken, except for the addition ofthe parasitic ring element 1980. The addition of the parasitic ringelement 1980 creates a more resonant RFID tag and increases the antennagain of the RFID tag 1902 in the normal to a plane (see plane 1200 ofFIG. 12) of the antenna system 1912.

FIG. 20 is a top plan view of an embodiment of an RFID tag 2002comprising an integrated circuit 2070 electrically coupled to an antennasystem 2012. The antenna system 2012 comprises a first arm 2011 and asecond arm 2013.

Referring now to the first arm 2011, a first segment 2084 iselectrically coupled to and extends generally in a first direction fromthe integrated circuit 2070. The first segment 2084 has a width W1 and alength L1. The first segment 2084 is electrically coupled to a curvedreturn segment 2088. The curved return segment 2088 extends from thefirst segment 2084 in a second direction generally upward and oppositefrom the first direction. The curved return segment 2088 has a width W3,a length L3 and a curvature C1. Together, the first segment 2084 and thereturn segment 2088 form a first convex portion 2033 of the antennasystem 2012.

Referring now to the second arm 2013, a first segment 2090 iselectrically coupled to and extends from the integrated circuit 2070 ina third direction generally opposite from the first direction. The firstsegment 2090 has a width W1 and a length L1. The first segment 2090 iselectrically coupled to a curved return segment 2094. The curved returnsegment 2094 extends from the first segment 2090 in a third directiongenerally downward from the first segment 2090 and in the firstdirection. The curved return segment 2094 has a width W3, a length L3and a curvature C1. Together, the first segment 2090 and the curvedreturn segment 2094 form a second convex portion 2037 of the antennasystem 2012.

Referring now to the antenna system as a whole, the first convex portion2033 and the second convex portion 2037 together form an S-shapedportion 2035 of the antenna system 2012. The S-shaped portion 2035 iselectrically coupled to the integrated circuit 2070 between the firstconvex portion 2033 and the second convex portion 2037.

Optional parasitic elements 2080 are positioned outside the curvedreturn segments 2088, 2094 of the first and second arms 2011, 2013 ofthe antenna system 2012. The parasitic elements have a width W7 and areseparated from the curved return segments 2088, 2094 of the antennasystem 2012 by a distance W8.

FIG. 21 is a top plane view of an embodiment of an RFID tag 2102comprising an RFID device 2106. The RFID device 2106 comprises anintegrated circuit 2170, and an antenna system 2112 comprising a firstarm 2111 electrically coupled to the integrated circuit 2170 and asecond arm 2113 electrically coupled to the integrated circuit 2170.

The first arm 2111 comprises a first segment 2184, a second segment2186, a third segment 2188, a fourth segment 2191 and a fifth segment2195. The first segment 2184 has a width W1 and a length L1, the secondsegment 2186 has a width W2 and a length L2, the third segment 2188 hasa width W3 and a length L3, the fourth segment 2191 has a width W9 and alength L7, the fifth segment 2195 has a width W10 and a length L8. Thesecond arm 2113 comprises a first segment 2190, a second segment 2192, athird segment 2194, a fourth segment 2193 and a fifth segment 2197. Thefirst segment 2190 has a width W4 and a length L4, the second segment2192 has a width W5 and a length L5, the third segment 2194 has a widthW6 and a length L6, the fourth segment 2193 has a width W11 and a lengthL9 and the fifth segment 2197 has a width W12 and a length L10.

The first segment 2184 of the first arm 2111 and the first segment 2190of the second arm 2113 extend from the integrated circuit 2170 ingenerally opposite directions. That is, the first segment 2184 of thefirst arm 2111 extends from the integrated circuit 2170 in a firstdirection and the first segment 2190 of the second arm 2113 extends fromthe integrated circuit 2170 in a second direction opposite from thefirst direction with respect to the integrated circuit 2170.

Referring now to the first arm 2111, the third segment 2188 is generallyparallel to the first segment 2184 and is electrically coupled to thefirst segment 2184 through the second segment 2186. The second segment2186 extends from the first segment 2184 in a third direction generallyperpendicular to the first direction. The third segment 2188 extendsfrom the second segment 2186 generally in the second direction. Thefourth segment 2191 is electrically coupled to the third segment 2188and extends from the third segment 2188 in a fourth direction generallyperpendicular to the second direction and opposite of the thirddirection. The fifth segment 2195 is electrically coupled to the fourthsegment 2191 and extends from the fourth segment in a fifth direction atan angle θ with respect to the fourth segment 2191 between zero and 90degrees. Thus, the first three segments 2184, 2186, 2188 of the firstarm 2111 have a C-shaped configuration forming a first convex portion2133 of the antenna system 2112 opening in the second direction.

Referring now to the second arm 2113, the third segment 2194 isgenerally parallel to the first segment 2190 and is electrically coupledto the first segment 2190 through the second segment 2192. The secondsegment 2192 extends from the first segment 2190 in the fourth directiongenerally perpendicular to the second direction and opposite the thirddirection. The third segment 2194 extends from the second segment 2192generally in the first direction. The fourth segment 2193 iselectrically coupled to the third segment 2194 and extends from thethird segment 2194 in the third direction. The fifth segment 2197 iselectrically coupled to the fourth segment 2193 and extends from thefourth segment 2193 in a sixth direction at an angle α with respect tothe fourth segment 2193 of between zero and 90 degrees. Thus, the firstthree segments 2190, 2192, 2194 of the second arm 2113 have a C-shapedconfiguration forming a second convex portion 2137 of the antenna system2112 opening in the first direction.

Referring now to the antenna system 2112 as a whole, the antenna systemhas an S-shaped configuration or portion 2135 formed from the firstconvex portion 2133 of the first arm 2111 and the second convex portion2137 of the second arm 2113. The antenna system 2112 is electricallycoupled to the integrated circuit 2170 along a central portion 2139 ofthe S-shaped portion 2135. As illustrated in FIG. 21, the S-shapedportion 2135 is rectilinear. In other words, the S-shaped portion 2135is comprised of straight segments coupled together at various angles.

A straight line B-B can be drawn which: intersects the first segment2184 and the third segment 2188 of the first arm 2111 of the antennasystem 2112; does not intersect the second segment 2186 of the first arm2111; and does not intersect the first segment 2190 of the second arm2113. A second straight line C-C can be drawn which: intersects thefirst segment 2190 and the third segment 2194 of the second arm 2113 ofthe antenna system 2112; does not intersect the second segment 2192 ofthe second arm 2113; and does not intersect the first segment 2184 ofthe first arm 2111.

Performance of an embodiment as illustrated in FIG. 21 was measured fora single-sided, 2 mil. polyester substrate 2103, a Philips G2 RFIDintegrated circuit or chip 2170 and flip-chip packaging with a one-ouncecopper antenna trace printed on the polyester substrate 2103, andwherein,

L1=L4=24 mm  (Eq. 29)

L2=L5=L7=L9=22 mm  (Eq. 30)

L3=L6=48 mm  (Eq. 31)

W1=W2=W3=W4=W5=W6=1 mm  (Eq. 32)

W9=W10=W11=W12=1 mm  (Eq. 33).

The embodiment was placed in a label (not shown) and affixed tocardboard (not shown). An 18-foot peak range was obtained at a resonantfrequency of 915 MHz and a range width from 890 to 950 MHz for aneleven-foot minimum range when measured normal to a plane (see plane1200 of FIG. 12) of the antenna system 2112. The antenna system 2112 hasdimensions of 48 mm by 48 mm, which provides a compact, S-shapedantenna.

FIG. 22 is a top plan view of an RFID tag 2202 comprising a dual-inputRFID device 2206 comprising an antenna system 2212 electrically coupledto an integrated circuit 2270. The antenna system 2212 comprises fourarms 2211, 2213, 2218, 2220. As illustrated, each arm 2211, 2213, 2218,2220 comprises a first segment 2284 having a width W1 and a length L1, asecond segment 2286 having a width W2 and a length L2, and a thirdsegment 2288 having a width W3 and a length L3. The first arm 2211 andthe second arm 2213 together form an S-shaped portion 2204 formed from afirst convex portion 2208 and a second convex portion 2210. The firstarm 2211 and the second arm 2213 are electrically coupled to theintegrated circuit 2270 separately and along a central portion 2209 ofthe S-shaped portion 2204. The first convex portion 2208 opens in afirst direction and the second convex portion 2210 opens in a seconddirection opposite the first direction.

The third arm 2218 and the fourth arm 2220 together form a secondS-shaped portion 2222 formed from a third convex portion 2224 and afourth convex portion 2226 of the antenna system 2212. The third arm2218 and the fourth arm 2220 are electrically coupled to the integratedcircuit 2270 separately and along a central portion 2228 of the secondS-shaped portion 2222. The second arm 2213 and the fourth arm 2220 areelectrically coupled to a common node 2230 of the integrated circuit2270. The third convex portion 2224 opens in a third direction and thefourth convex portion 2226 opens in a fourth direction opposite thethird direction. The second S-shaped portion 2222 is rotated ninetydegrees with respect to the first S-shaped portion 2204 in a plane ofthe antenna system 2212 (see plane 1200 in FIG. 12). The segments 2284,2286, 2288 of the arms 2211, 2213, 2218, 2220 may have different widthsW1, W2, W3 and lengths L1, L2, L3.

In one embodiment, the RFID tag 2202 illustrated in FIG. 22 may beconstructed using a single-sided, 2 mil. polyester substrate 2203 andflip-chip packaging with one-ounce copper trace material printed on thesubstrate 2203 to form the arms 2211, 2213, 2218, 2220 of the antennasystem. Based on the measurements conducted on the embodimentillustrated in FIG. 15, if the following parameters are employed,

L1=L3=40 mm  (Eq. 34)

L2=30 mm  (Eq. 35)

W1=0.5 mm  (Eq. 36)

W2=W3=10 mm  (Eq. 37),

the embodiment illustrated in FIG. 22 has a theoretical peak range of 38feet at a resonant frequency of 915 MHz with improvedomni-directionality over the embodiment illustrated in FIG. 15 and withdimensions of approximately 80 mm by 80 mm.

FIG. 23 is a top plan view of an embodiment of an RFID tag 2302 asillustrated in FIG. 22 with an optional parasitic loop 2380 printed onthe substrate 2303 around the four arms 2311, 2313, 2318, 2320 of theantenna system 2312. The four arms 2311, 2313, 2318, 2320 of the antennasystem 2312 are coupled to an integrated circuit 2370. An embodiment maybe constructed using a single-sided, 2 mil. polyester substrate 2303 andflip-chip packaging with one-ounce copper trace material printed on thesubstrate 2303 to form the arms 2311, 2313, 2318, 2320 of the antennasystem. Based on the measurements conducted on the embodimentillustrated in FIG. 15, if the following parameters are employed,

L1=L3=40 mm  (Eq. 38)

L2=30 mm  (Eq. 39)

W1=0.5 mm  (Eq. 40)

W2=W3=10 mm  (Eq. 41)

W7=5 mm  (Eq. 42)

W8=1 mm  (Eq. 43),

the embodiment illustrated in FIG. 23 has a theoretical peak range ofgreater than 40 feet at a resonant frequency of 915 MHz with improvedomni-directionality over the embodiment illustrated in FIG. 15 and withdimensions of approximately 102 mm by 102 mm.

FIG. 24 is a top plan view of an embodiment of an RFID tag 2402comprising a first RFID device 2406, a second RFID device 2408 and acontroller 2410. The first RFID device 2406 comprises circuitry 2407(such as the power system 114 and data system 120 of FIG. 1) on anintegrated circuit 2470 electrically coupled to an antenna system 2412comprising a first arm 2411 and a second arm 2413. The second RFIDdevice 2408 comprises circuitry 2409 (such as the power system 128 anddata system 134 illustrated in FIG. 1) on the integrated circuit 2470electrically coupled to an antenna system 2426 comprising a first arm2418 and a second arm 2422. The first RFID device 2406 and the secondRFID device 2408 are communicatively coupled to the controller 2410. Thefirst RFID device 2406 may be configured for operation in a firstfrequency range or in accordance with a first communications protocolwhile the second RFID device 2408 is configured for operation in asecond frequency range or in accordance with a second communicationsprotocol. The controller 2410 may control one or more of the RFIDdevices 2406, 2408 based on a state of the RFID tag 2402. The differencein radio-frequency electrical lengths of arm pairs 2411, 2413 and 2418,2422 facilitates a dual frequency operation of RFID tag 2402.

The RFID tags of the embodiments described above may be readilyconstructed by printing traces of the portions or of the segments of theantenna systems (see, e.g., antenna system 112 in FIG. 1) on a substrate(see, e.g., substrate 103 in FIG. 1), such as a board, and electricallycoupling the antenna systems to other components of the radio-frequencyidentification devices, such as an integrated circuit (see, e.g.,integrated circuit 770 in FIG. 7). The performance characteristics ofRFID tags constructed using this method may be readily modified byadjusting the width, lengths, positioning, and, where desired, thecurvature of the printed traces used to form the segments of the antennaportions. In addition, parasitic elements of various widths, lengths andcurvatures may be positioned around the segments of the antenna system.

FIG. 25 illustrates a system 2532 comprising a controller 2534 and atrace printer 2536 that may be used to manufacture RFID tags, such asthe embodiments described above. The controller 2534 comprises aprocessor 2538 and a memory 2540 and is configured to control the traceprinter 2536. The system 2532 may be readily configured to producemultiple RFID tags in a single manufacturing run. Each RFID tag, andeach RFID device on an RFID tag, produced during a run may have thesame, or different, performance characteristics. In addition,performance characteristics may be easily modified between manufacturingruns by adjusting the parameters of the printed traces forming theantenna segments.

One particularly advantageous application of embodiments of the RFIDtags discussed above is in animal tracking, which uses both ISO 1800-6Bin the 915 MHz band and ISO 11784/11785 (the International Standard forRadio Frequency Identification of Animals) in the 134.2 KHz band. Afirst RFID device could be configured to operate in accordance with ISO1800-6B in the 915 MHz band and a second RFID device could be configuredto operate in accordance with ISO 11784/11785 in the 134.2 KHz band. Inaddition, it may be possible to locate an animal with a first RFIDdevice (such as RFID device 606 illustrated in FIG. 6) configured tooperate at a first frequency, and then decide whether to use a secondRFID device (such as RFID device 608 illustrated in FIG. 6 and/or RFIDdevice 664 illustrated in FIG. 6) configured to operate at a differentfrequency to retrieve data.

The term “computer-readable medium” as used herein refers to any mediumthat participates in providing instructions to a system or a processorfor execution. Such a medium may take many forms, including but notlimited to, non-volatile media, volatile media, and transmission media.Non-volatile media includes, for example, hard, optical or magneticdisks. Volatile media includes dynamic memory. Transmission mediaincludes coaxial cables, copper wire and fiber optics. Transmissionmedia can also take the form of acoustic or light waves, such as thosegenerated during radio wave and infrared data communications.

Common forms of computer-readable media include, for example, a floppydisk, a flexible disk, hard disk, magnetic tape, or any other magneticmedium, a CD-ROM, any other optical medium, punch cards, paper tape, anyother physical medium with patterns of holes, a RAM, a PROM, EPROM andan EEPROM, a FLASH-EPROM, any other memory chip or cartridge, a carrierwave, or any other medium from which a computer can read.

Various forms of computer readable media may be involved in carrying oneor more sequences of one or more instructions to a processor forexecution. For example, the instructions may initially be carried on amagnetic disk of a remote computer. The remote computer can load theinstructions into its dynamic memory and send the instructions over atelephone line using a modem. A modem local to computer system canreceive the data on the telephone line and use an infrared transmitterto convert the data to an infrared signal. An infrared detector coupledto a system bus can receive the data carried in the infrared signal andplace the data on system bus. The system bus carries the data to systemmemory, from which a processor retrieves and executes the instructions.The instructions received by system memory may optionally be stored onstorage device either before or after execution by the processor.

Although specific embodiments of and examples for the RFID tags,devices, methods, and articles are described herein for illustrativepurposes, various equivalent modifications can be made without departingfrom the spirit and scope of this disclosure, as will be recognized bythose skilled in the relevant art. The various embodiments describedabove can be combined to provide further embodiments.

These and other changes can be made to the invention in light of theabove-detailed description. In general, in the following claims, theterms used should not be construed to limit the invention to thespecific embodiments disclosed in the specification and the claims.Accordingly, the invention is not limited by the disclosure, but insteadits scope is to be determined entirely by the following claims.

1-38. (canceled)
 39. A method of operating a radio-frequencyidentification system, comprising: receiving a first response signalfrom a first radio-frequency identification device of a radio-frequencyidentification tag in response to an interrogation signal; when thefirst response signal is received, processing the first response signal;determining whether a second response signal is received from a secondradio-frequency identification device of the radio-frequencyidentification tag; and when the first response signal is received andit is determined that the second response signal is not received,initiating error processing.
 40. The method of claim 39 wherein thefirst response signal is in a first frequency range and the secondresponse signal is in a second frequency range different from the firstfrequency range.
 41. The method of claim 40 wherein the first frequencyrange is lower than the second frequency range.
 42. The method of claim39 wherein the interrogation signal comprises a first component signalat a first frequency and a second component signal at a second frequencydifferent from the first frequency.
 43. The method of claim 39 whereindetermining whether the second response signal is received comprisesdetermining whether the second response signal is received within adefined period of time of receipt of the first response signal. 44.-86.(canceled)